The invention relates to classifying pixels of an image.
A person responsible for inspecting a manufactured item (e.g., an electronic component) for defects typically learns about the item and objects included in the item (e.g., electrical terminals on an electronic component) by visually examining the item. When inspection is automated, information about the item is obtained by automated analysis of an image of the item. The obtained information may include the location of the objects included in the item and the size and shape of the objects. An automated inspection system typically obtains the location of each object by searching the image for a distinguishing characteristic of the object, such as a specific color or shape. If the image's coloring is difficult to predict (e.g., due to variations in the tint or intensity of the lighting used to illuminate the object) or the specific shape is present only in an altered form (e.g., due to a rotated orientation of the object as represented in the image), it may be difficult for the automated system to locate the object in the image.
Examples of manufactured items appropriate for inspection include ball grid array devices, micro-ball grid arrays, flip chips, and chip-scale packages (together called "BGAs"). BGAs share a common feature in that the contacts on the device are metallic balls that are mounted on one side of the device for forming electrical connections between the package's integrated circuit and a printed circuit board.
To work properly, the balls of BGAs should be properly located to connect to the pads on the circuit board. The balls also should be properly formed (i.e., should have a spherical shape and neither too much nor too little solder, to allow an acceptable electrical connection). The balls also should not be connected by extraneous solder or other material in the spaces between the balls. If these conditions are not met, the BGA may fail to make proper electrical connections or durable physical bonds.
Unlike traditional leaded devices that have contacts exposed on perimeters where some types of defects (e.g., solder bridges or missing solder) can be detected even after soldering, BGAs are harder to inspect after mounting on a circuit board. BGAs therefore are inspected before mounting, either in fully-assembled form or by inspection of ball arrays that are about to be attached to the packages of integrated circuits.
Inspections are done on other types of products, e.g., pill blister packs and candy sampler boxes.